Conventionally, Patent Literature 1 has disclosed a firing condition-detecting device for an internal-combustion engine that overlaps in-cylinder pressure signals in respective combustion chambers detected by in-cylinder pressure detecting means to determine a misfire condition with a misfire determining index number calculated based on the overlapped in-cylinder pressure signals.
As stated above, when each of the in-cylinder pressures in a plurality of the combustion chambers is overlapped, a significant change is recognized in symmetry property of a signal waveform before and after a top dead center, in accordance with presence or absence of a misfire. Therefore, the misfire determination can be made in the whole region of combustion in the internal combustion engine.
In the conventional, firing condition-detecting device, however, the misfire determining index number is basically calculated by integrating an in-cylinder pressure detected by the in-cylinder pressure detecting means, per unit of a minute crank angle. Consequently, a load on calculation in the conventional firing condition-detecting device is substantial, so that it is not actually easy to apply the conventional device to an internal combustion engine for a vehicle and the like, for example.
[Patent Literature 1] Japanese Patent Application Laid-open No. 11-82150